Concerns have been raised that deformation of
acetabular shells may disrupt the assembly process of modular prostheses.
In this study we aimed to examine the effect that the strength of
bone has on the amount of deformation of the acetabular shell. The
hypothesis was that stronger bone would result in greater deformation.
A total of 17 acetabular shells were inserted into the acetabula
of eight cadavers, and deformation was measured using an optical
measuring system. Cores of bone from the femoral head were taken
from each cadaver and compressed using a materials testing machine.
The highest peak modulus and yield stress for each cadaver were used
to represent the strength of the bone and compared with the values
for the deformation and the surgeon’s subjective assessment of the
hardness of the bone. The mean deformation of the shell was 129
µm (3 to 340). No correlation was found between deformation and
either the maximum peak modulus (r² = 0.011, t = 0.426, p = 0.676) or
the yield stress (r² = 0.024, t = 0.614, p = 0.549) of the bone.
Although no correlation was found between the strength of the bone
and deformation, the values for the deformation observed could be
sufficient to disrupt the assembly process of modular acetabular
components. Cite this article:
Modular un-cemented acetabular components are used in over 50% of UK hip replacements. Mal-seating of hard liners has been reported as a cause of failure which may be a result of errors in assembly, but also could be affected by deformation of the acetabular shell on insertion. Little information exists on in vivo shell deformation. Previous work has confirmed the importance of shell diameter and thickness upon shell behaviour, but mostly using single measurements in models or cold cadavers. Exploration of deformation and its relaxation over the first twenty minutes after implantation of eight generic metal cups at body temperature. Using a previously validated cadaveric model at controlled physiological temperature with standardised surgical technique, we tested the null hypothesis that there was no consistency for time dependent or directional change in deformation for a standard metal shell inserted under controlled conditions into the hip joint. Eight custom made titanium alloy (TiAl6V4) cups were implanted into 4 cadavers (8 hips). Time dependent cup deformation was determined using the previously validated ATOS Triple Scan III (ATOS)
